Ia antigen expression on the developing mouse embryo and placenta.

The expression of I region controlled antigens on the mouse embryo and placenta has been investigated using immuno-peroxidase labelling and a mixed haemadsorption assay. The results indicate that Ia antigens are absent from selected pre- and post-implantation embryonic and trophoblastic tissues and from the trophoblast of the definitive placenta. In contrast, cells derived from the peri-placental maternal decidual tissues are Ia antigen-positive. The findings are discussed in relation to the allograft status of the conceptus and the identity and functional significance of the Ia-bearing maternal cells at the foeto-maternal interface.